U.S. patent number 4,512,025 [Application Number 06/443,982] was granted by the patent office on 1985-04-16 for increasing capacity of baseband digital data communication networks.
This patent grant is currently assigned to The United States of America as represented by the United States. Invention is credited to Robert S. Frankel, Alexander Herman.
United States Patent |
4,512,025 |
Frankel , et al. |
April 16, 1985 |
Increasing capacity of baseband digital data communication
networks
Abstract
This invention provides broadband network capabilities for
baseband digital collision detection transceiver equipment for
communication between a plurality of data stations by affording
simultaneous transmission of multiple channels over a broadband
pass transmission link such as a coaxial cable. Thus, a fundamental
carrier wave is transmitted on said link, received at local data
stations and used to detect signals on different baseband channels
for reception. For transmission the carrier wave typically is used
for segregating a plurality of at least two transmission channels
into typically single sideband upper and lower pass bands of
baseband bandwidth capability adequately separated with guard bands
to permit simple separation for receiving by means of pass band
filters, etc.
Inventors: |
Frankel; Robert S. (Centereach,
NY), Herman; Alexander (Hertzelia, IL) |
Assignee: |
The United States of America as
represented by the United States (Washington, DC)
|
Family
ID: |
23762989 |
Appl.
No.: |
06/443,982 |
Filed: |
November 23, 1982 |
Current U.S.
Class: |
375/257; 370/485;
375/270; 455/527 |
Current CPC
Class: |
H04L
12/2801 (20130101) |
Current International
Class: |
H04L
12/28 (20060101); H04B 003/50 () |
Field of
Search: |
;340/825.5 ;375/43,36
;455/15,16,47,51,58 ;370/30,69.1,121,71,72,124,74 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
"A Low-Loss, Wideband Transmitter Multiplexer", Smith 1973 IEEE
International Microwave Symposium, Boulder, Colorado..
|
Primary Examiner: Safourek; Benedict V.
Attorney, Agent or Firm: Myles; Vale P. Gottlieb; Paul A.
Hightower; Judson R.
Government Interests
BACKGROUND OF THE INVENTION
The invention described herein was made or conceived in the course
of, or under a contract with, the U.S. Department of Energy.
Claims
We claim:
1. A digital data communication network system with collision
prevention means including a plurality of stations using a
particular assigned frequency bandwidth spectrum of a transmission
link communicating digital signals between (a) said plurality of
digital data stations, said collision prevention means being
operable to prevenf interference by concurrent use of the same
frequency by more than one of said stations, comprising in
combination,
means including a clear channel detector for enabling the
transmitting of digital signal communications from at least two of
said digital data stations respectively in separate ones of said
frequency bands carried simultaneously by locally choosing one of
such frequency bands within the assigned link bandwidth having a
clear channel as identified by said detector, and
receiving means tuned to a selected one of said separate frequency
bands carried simultaneously and including collision prevention
means responsive to said detector for enabling reception on a clear
channel of one of said digital communications transmitted within
that assigned frequency band over said transmission link.
2. A system as defined in claim 1 wherein said means for
transmitting includes modulating means for modulating a carrier
wave with two signals to be transmitted to produce the respective
signals contained within said assigned frequency band with the
carrier wave and modulated sidebands thereof being of a frequency
within the transmission bandwidth of the assigned transmission
line, and sideband processing means in said modulating means tuned
to create separate sideband signals for said carrier wave for said
two signals to be within said separate frequency bands that can be
carried over said assigned transmission link without interference
therebetween.
3. A system as defined in claim 2 including means for transmitting
the unmodulated carrier wave into said transmission link, and means
respectively in the transmitting means and detection means located
at a digital data station for deriving the carrier wave from the
transmission link and processing it locally for transmitting and
receiving the separate frequency bands at that digital station.
4. A system as defined in claim 1 wherein said transmission link is
a single coaxial cable.
5. A system as defined in claim 1 wherein said transmission link
comprises two coaxial cables each adapted to communicate said
digital signals between said data stations,
means for transmitting signals in separate ones of said frequency
bands carried simultaneously onto respective ones of the coaxial
cables,
and a data station coupled to both said cables to receive therefrom
and transmit thereinto said digital signals and including means for
selecting a respective one of said cables for a clear channel
communication link to another digital station coupled thereto.
6. A system as defined in claim 5 including means for transmitting
a carrier wave within the coaxial cable transmission bandwidth into
a single said cable, means in said data station coupled to both
cables to receive said carrier wave, and means in said data station
coupled to both cables responsive to said carrier wave for
respectively receiving and transmitting said digital data signals
on a single one of said frequency bands.
Description
This invention relates to digital data communication networks and
more particularly it relates to increasing the data processing
capability of baseband digital data communication systems of the
type set forth in the U.S. Pat. No. 4,063,220 to Robert M. Metcalfe
et al., issued Dec. 13, 1977, known by the Xerox Corporation
tradename "Ethernet".
The aforesaid Metcalfe patent has led to commercialized digital
data communication systems between two different computers, office
machines, or the like. These systems have a restricted bandwidth of
communication known in the trade as baseband systems. A
disadvantage of these systems with the collision prevention
technique of listening for a clear channel before talking not
heretofore resolved is that communications are limited to a single
narrow bandwidth communication channel. This has led to alternative
broadband systems which are more complex and require processing of
analog data in order to offer more channels of communication. A
background on these alternatives is set forth in an article by
Kenneth Klee et al., entitled "Battle of the Networks" published in
Datamation, March 1982. Thus, the state of the art is such that
there only is provided a system choice between a broadband network
or a single channel baseband network.
As clearly set forth in the above article, it has been heretofore
deemed in the art inconsistent to adapt a digital baseband network
with collision prevention means to any compatible broadband
capability to process two or more signals simultaneously.
It is therefore an object of this invention to improve the digital
baseband communication network art by providing broadband
multiple-channel communication capabilities while retaining the
advantages of collision prevention.
Other objects, features and advantages of the invention will be
found throughout the following description, drawing and claims.
DISCLOSURE OF THE INVENTION
Thus in accordance with this invention a baseband digital
communication network system with collision prevention means is
provided for handling two or more communications simultaneously
over a transmission link, thereby affording the advantages of
broadband analog communication systems.
In a preferred embodiment a carrier wave is transmitted over the
transmission link and serves at a data station coupled with the
link to segregate both transmitted and received signals into at
least two separate bands so that at least two simultaneous signal
channels may be used in the network while operating with the
network collision prevention means.
Thus, for example, two signal bands with appropriate guard bands
therebetween (and between other signals transmitted on the link)
may comprise the upper and lower single sideband transmission of
the two respective bands. Such bands are separable by band
filtering and demodulation by network receivers. Also transmission
is readily accomplished by modulating and filtering to send only a
single (upper or lower) sideband through the transmission link,
which is preferably a coaxial cable, but also may comprise a radio
link, optical link, etc.
Accordingly, each network data station is readily convertible to
communicate with and process a plurality of at least two data bands
to thereby increase the data transmission capabilities of tne
network as comparable with broadband network systems without
collision prevention, wherein simultaneous signals may be conveyed
and intercepted along the network.
BRIEF DESCRIPTION OF THE DRAWINGS
In the accompanying drawings:
FIG. 1 is a block system diagram of a binary baseband data
transmission network embodying the invention;
FIG. 2 is a graph with frequency as the abscissa showing the
relationships of a carrier wave, two data transmission bands and a
transmission channel passband characteristic as afforded by the
teachings of this invention;
FIGS. 3 and 4 are block system diagram embodiments of a network and
data processing station as afforded by this invention;
FIG. 5 is a block diagram of a carrier processing portion of the
system afforded by this invention;
FIG. 6 is a block diagram of a signal receiving portion of the
system afforded by this invention;
FIG. 7 is a block diagram of a signal transmitting portion of the
system afforded by this invention; and
FIG. 8 is a block diagram of the interface portion of the system
afforded by this invention with a baseband digital communication
network of the type employing collision prevention means.
THE PREFERRED EMBODIMENTS
By reference to FIG. 1, it may be seen that a broadband
transmission link 15 such as a coaxial cable, radio system or
optical system serves to connect a plurality of individual data
station transceivers 16A, 16B, 17, 18, etc. for communicating
digital data therebetween in a baseband collision detection mode.
The channel 15 bandwidth characteristic (or available spectrum
band) is sufficient to carry simultaneously transmissions in a
plurality of two or more (n) baseband channels between the data
stations.
The state of the art heretofore has required a separate
transmission channel (coaxial cable) 15 for each baseband channel
and the collision detection mode limits transmission on that
channel to a single message. That is, each data station in its
interface equipment 20, etc. inquires to see if the channel is in
use before a message is communicated to another station along the
line, as set forth in the Metcalfe patent, supra.
As seen in the FIG. 1 system of this invention, however, the
transmission link is afforded a mode of operation permitting more
data to be processed, and faster access time, by simultaneous
transmission of a plurality of baseband channels n to which the
data stations 16, 17, 18, etc. have access. This also provides more
system flexibility in the data stations, at the cost of some
relatively simplified filtering or selection equipment as part of
the interfacing 20 between the transceivers 16, 17, 18 and the
transmission link 15. Thus, for example, a "busy" data station 16
may have two transceivers 16A, 16B each with the capacity to
communicate on multiple channels (CH #1 and #2). Data station 17
could be a single channel station communicating on channel #1 only,
and similarly station 18 could communicate on channel #2. Other
stations (B to L, etc.) along the line thus can have considerable
flexibility without disturbing the system mode or limiting the
ability to communicate single channel wise with other stations in
the manner available to the art prior to this present
invention.
One specific preferred mode of operation is exemplified by the
bandwidth graph of FIG. 2 drawn on a frequency (f) abcissa. Thus,
typically a carrier frequency (fo) of 80 MHz is single sideband
modulated with the baseband data of limited bandwidth to produce a
properly guarded lower sideband first channel 21 and an upper
sideband second channel 22 both falling within the transmission
bandwidth 23 of the broadband transmission link. These two separate
channels, CH #1 and CH #2 corresponding to notation of FIG. 1,
provide the network capability of simultaneous communications not
heretofore feasible with networks providing a collision prevention
mode of transmission of digital signals. The treatment of data is
done by state of the art modulation and multiplexing techniques,
such as set forth in U.S. Pat. No. 3,202,762 to M. R. Aaron et al.,
Aug. 24, 1965; U.S. Pat. No. 3,842,352 to W. E. Cote, Oct. 15,
1974; and U.S. Pat. No. 3,914,554 to H. Seidel, Oct. 21, 1975.
Mixing, modulating, multiplexing and filtering data at required
frequency bands is achieved by simple state of the art equipment as
described for example by an article published in the Digest of
Technical Papers of the 1973 IEEE International Microwave Symposium
at Boulder, Colo., June 4 to 6, 1973 entitled "A Low-Loss, Wideband
Transmitter Multiplexer" by J. I. Smith and R. E. Fisher of Bell
Laboratories. Thus, to better set forth the nature and spirit of
this invention, the network features are set out in block diagram
form throughout the remaining figures.
A simplified system is attained in the two cable (15L, 15R) network
of FIG. 3. A coupler 30 is used for receiving (Rx) signals from the
cables or transmitting (Tx) signals onto the cables from the
various station units. Each cable 15L and 15R then may comprise a
different data channel corresponding to the aforesaid CH #1 and CH
#2. Note that a single carrier frequency generator 31 is coupled to
a single cable 15L for use in the mode described in FIG. 2.
The carrier is thus detected by receiver 32 and amplified at
carrier amplifier 33 for local use in transmitting and receiving
operations, and in this manner may be used for synchronous
relationships (if used) in the system. The single transmitter 35
then receives the carrier along lead 34 for modulation respectively
of upper or lower sideband (depending upon the channel 15L or 15R
accessibility) which is coupled to the respective cable by
corresponding band-pass filters 36L and 36R permitting only the
desired channel to enter the corresponding cable (as directed from
the logic board 37 along lead 38).
Receivers 32 and 39 are coupled to the respective cables 15L, 15R
in the manner described in the Metcalfe patent, supra and provide
via logic board 37 the respective collision signals 40 and received
data 41 to digital processor 42 for timed release of data to be
transmitted 43. Clearly the digital processor has access to either
of two data base channels along the respective coaxial cables 15L,
15R, thereby to give improved access time and other advantages of a
broadband system while retaining the significant advantages of the
collision detection mode.
In order to receive and segregate (demultiplex) the data from the
respective two (or more) baseband channels (e.g. 15R, 15L), the
carrier signal from amplifier 33 is carried by lead 45 to receivers
32, 39 and respectively heterodyned by state of the art techniques
to detect the upper and lower sideband digital data transmitted
over the link 15. The logic board 37 will then direct the selected
digital data through the baseband pass receiving link of twisted
pair 41 into digital processor 42.
This network has advantages of simplified hardware requirements to
achieve the broadband capabilities, essentially comprising: a
second receiver 32, a logic board 37, a carrier amplifier 33 and
filters 36 (or switching means) for coupling the transmitter 35 to
a selected one of cables 15R or 15L. There is no disadvantage to
the two cable connection over the state of the art since it has
only been contemplated heretofore that the baseband
collision-detecting digital signal is sent on each communication
link at a time. However, as shown in FIG. 4, a single cable link
may be used at the expense of a little more complicated logic (37')
and a second transmitter 35A.
The conversion equipment for adapting the baseband collision
detection network to broadband collision detection mode and
capabilities is typically that set forth in FIGS. 5 to 8.
The carrier amplifier circuit 33 of FIG. 5, therefore serves to
derive with the narrow band pass filter 50 the fundamental carrier
wave (fo) from the coaxial link 15 (15L), which is amplified (51)
and limited (52) before processing in logic circuit 37.
In FIG. 6, typical receiver input filter circuits are shown. In
essence, the carrier signal is used at mixer 60 with the broadband
signal from band pass filter 61 to derive the baseband signal
filtered at narrow pass filter 62, e.g. a low pass filter for
deriving the lower sideband of FIG. 2. The transmitter similarly in
FIG. 7 mixes the carrier signal at mixer 70 lead 71 with the
signals to be transmitted at lead 72, and derives the upper or
lower single sideband at filter 73 for transmission.
The logic board in FIG. 8 processes signals from the two receivers
for the two baseband channels on lines 81, 82, through the
collision detector 83 of the Metcalfe patent, supra, to derive the
collision signal 40 and to pass the received digital signals
through OR circuit 84 to receiver line 40. Output transmitted
signals on line 85 as detected at 86 are passed to the carrier
amplifier on line 87 for mixing as shown in FIG. 7.
Other variations in mixing and processing signals are within the
skill of those in the art using the present state of the art. Those
novel features of the invention believed descriptive of the scope
and spirit of the invention are set forth with particularity in the
claims.
* * * * *